Wettability alteration of carbonate rock by nonionic surfactants in water-based drilling fluid

The influx of solid or liquid particles of drilling mud into the pores of rock or mud loss phenomenon and clay swelling can sometimes lead to severe productive formation damage and cause to wettability alterations of reservoir rock from hydrophilic to oleophilic. Therefore, designing an appropriate fluid that is compatible with formation fluids and could reduce reservoir damage and increase the productivity of wells is very important. The two main mechanisms of surfactants are reduction of the surface tension and wettability alteration of rock reservoir that are effective in taking the oil. Regarding the importance of the wettability in reservoir productivity, this article is aimed to study the effect of nonionic surfactants polyethylene glycol (PEG) in the presence of acrylamide hydrolysis (PHPA) in water-based drilling fluids. For the measurement of wettability alterations, measurements of contact angle as a quantitative method and measurement of clay swelling, weight difference was used. The calcium carbonate was used as a representative of the reservoir rock. The experiment was designed so that the parameters of drilling fluid (fluid loss control, rheology, chloride, potassium chloride, pH, temperature, PEG and PHPA volume percent) are close to the reservoir. In order to simulate reservoir conditions after contact of calcium carbonate with drilling fluid, we put the sample in cylinder containing drilling fluids, and for more simulation of reservoir conditions, the test was repeated at 80 degrees C without the presence of surfactants and in the presence of surfactant. The distilled water and oil in the reservoir were used to obtain the contact angle. The obtained results reveal that since the reservoir is carbonate and hydrophilic, drilling fluid (without surfactant) makes the reservoir to go into oleophilic state where drilling fluid in the presence of surfactant causes the reservoir to go into hydrophilic state which will follow by reducing formation damage and increasing oil production.